A novel type of mass spectrometer has been developed and incorporated into a bioanalytical system with capabilities for sample introduction by GC, HPLC or probe. This instrument does not have a heated filament, and mass analysis can be carried out for both positive and negative ions. It is proposed to use this experience to design the next generation of bioanalytical systems, with capabilities of operating at 0.01 or 1 Torr, or at 1 atm. Emphasis will be placed on negative ion mass spectrometry; this is a major new area of research in mass spectrometry. The objective is to achieve capabilities for the quantitative analysis of human fluids with picogram and subpicogram samples. The applications chosen for study are all instances in which analytical data are required for diagnosis or treatment, or for toxicity studies.